The research has been divided into the following four integrated components: (1) Instrumentation - Completion of the development of "State-of-the Art" Instrumentation to rapidly obtain, on-line and stand-alone at all age groups, electrocardiographic low noise body surface potential color coded maps (BSPM) utilizing 180 passive electrodes with active cables. Insuring optimal safety in obtaining BSPM simultaneous with indwelling cardiac electrode catheters. (2) Clinical Studies - four major subprojects. a) Correlations of simultaneously obtained BSPM with endocardial electrophysiological studies (EPS), with analysis of spread of activation from known positioned stimulated activation during catheterization; b) Correlations of simultaneously obtained BSPM with spread of activation from known positioned epicardial pacemakers; c) Continued development of a normal quantified data base for P, QRS, ST-T, as well as development of maximal knowledge of BSPM's on a large number of children with varying pathology. Correlations with Frank VCG plus M Mode and 2D Echo; d) Correlation of quantified BSPM's in adults with remote myocardial infarction undergoing cardiac catheterization involving coronary angiography and ventriculography, plus 12 lead simultaneous standard ECG, Frank VCG, and Positron Emission Tomography (PET). (3) Image Measurements - Investigation of optimal imaging and display of BSPM data including determination of the effects of artifacts and system bandwidth upon the measurements of map features. Develop a systematic approach to automatic measurements of the map features which encode clinical information. (4) Biophysical Studies - a) Inverse Electrocardiography Methods for reconstructing epicardial potentials from body surface potential distributions utilizing the multipole expansion approach will be developed and tested. The reconstructed epicardial maps will aid in the interpretations of BSPM's; b) Forward Problem - An interactive computer model of the electrocardiographic forward problem for realistic heart and torso geometry is being developed. The model will contain the specialized conduction tissue and will generate isochrones, epicardial potentials, and body surface potential maps (BSPM's). This model will be used to simulate BSPM's in normal and abnormal conditions and will serve as an additional tool for the interpretation of the maps.